GENETIC ARCHITECTURE OF SEED YIELD AND ITS COMPONENT CHARACTERS IN F1 AND F2 GENERATIONS OF CASTOR (Ricinus communis L.) 2951
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Date
2019-09
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JAU, JUNAGADH
Abstract
The experimental material, consisting of 101 entries including 10 parents,
45 crosses, 45 F2s and one check hybrid (GCH 7) was raised in a Randomized Block
Design with three replications at the Main Oilseeds Research Station, JAU, Junagadh
during kharif 2016-17. The objectives of this investigation were to study the nature
and magnitude of heterosis and inbreeding depression, general combining ability
effect of parents, specific combining ability effect of hybrids, nature and magnitude of
gene action involved and genetic components of variation for seed yield per plant and
its attributing characters.
The results revealed that the mean squares due to genotypes were highly
significant for all the characters. The mean squares due to parents, hybrids and F2s
were highly significant for all the characters except for number of nodes up to primary
raceme in parents. The mean squares due to parents vs hybrids differed significantly
for all the characters, while the mean squares due to parents vs F2s were found
significant for days to 50% flowering of primary raceme, days to maturity of primary
raceme, plant height up to primary raceme, number of effective branches per plant,
100-seed weight and seed yield per plant. The results thus, indicated the presence of
considerable amount of genetic variability in the material studied and its suitability for
the study of manifestation of heterosis and genetic parameters involved in the
inheritance of different traits in castor.
The results revealed that the best three hybrids identified on the basis of per
se performance and standard heterosis for seed yield per plant viz., JI 368 x RG 2787,
DPC 17 x SKI 343 and DPC 17 x JI 353 also depicted significant positive standard
heterosis over GCH 7 for important yield contributing traits i.e. JI 368 x RG 2787
manifested significant standard heterosis for days to 50 % flowering of primary
raceme, days to maturity of primary raceme, oil content and seed yield per plant; DPC
17 x SKI 343 for days to 50 % flowering of primary raceme, days to maturity of primary
raceme, number of nodes up to primary raceme and seed yield per plant and DPC 17 x
JI 353 for days to 50% flowering of primary raceme, days to maturity of primary
raceme, plant height, number of nodes up to primary raceme, number of capsules on
primary raceme and seed yield per plant. This emphasized that high degree of
heterosis for seed yield might be attributed to the heterosis observed for the component Abstract
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characters. In the present study, five crosses viz., DPC 17 x JI 368, DPC 17 x JI 372,
JI 411 x JI 372, DCS 85 x JI 372 and DCS 85 x PCS 124 displayed significant
negative heterobeltiosis and standard heterosis simultaneously for days to 50%
flowering of primary raceme, days to maturity of primary raceme, plant height up to
primary raceme and number of nodes up to primary raceme. These high heterotic
crosses may be considered as potential and be exploited in breeding for the
development of early maturity and dwarf genotypes in castor.
In the present study, positive significant (desirable) inbreeding depression
was observed only for number of nodes up to primary raceme. While, negative
significant (desirable) inbreeding depression was observed for some the characters
viz., length of primary raceme, effective length of primary raceme, number of effective
branches per plant, number of capsules per plant and 100-seed weight. None of the
crosses showed significant inbreeding depression for seed yield per plant which is
highly desirable.
The analysis of variance for combining ability revealed that GCA and SCA
variances were significant for all the eleven characters in both the generations
reflecting the importance of both additive and non-additive genetic variances for
controlling these traits. The ratio of GCA/SCA variances was found more than unity
for effective length of primary raceme in F1 indicating the predominance of additive
genetic components of variation. Days to 50 % flowering of primary raceme, days to
maturity of primary raceme, plant height up to primary raceme, number of nodes upto
primary raceme, length of primary raceme, number of capsules on primary raceme,
number of effective branches per plant, 100-seed weight, oil content and seed yield per
plant, the GCA/SCA ratio was less than unity in both the generations, suggesting the
predominance of non-additive gene action for the inheritance of these traits and
emphasized the utility of hybrid breeding approach to exploit existing heterosis in the
castor.
None of the parents was found good general combiner simultaneously for
all the traits in both the generations. Among the parents, PCS 124, JI 353 and JI 368
in F1 generation and JI 353 and DPC 17 in F2 generation exhibited good general
combining ability effect for seed yield per plant.
The best three hybrids on the basis of significant positive sca effect for seed
yield per plant were JI 368 x RG 2787 (good x average combiners), DPC 17 x SKI
343 (average x average combiners) and JI 411 x SKI 215 (poor x poor combiners) in
F1 generation. While in F2 generation, the top high yielding hybrids DPC 17 × SKI
215 (good x average combiners), DPC 17 × SKI 343 (good x average combiners) and
DPC 17 x RG 2787 (good x average combiners), with significant heterobeltiosis as
well as standard heterosis, also depicted significant sca effect for seed yield per plant.
In facts, in most of the crosses, the best specific combinations for different characters
were either good x good, good x poor, average x average, average x poor or poor x
poor general combiners. It indicated additive x additive, additive x dominance and
dominance x dominance type of gene interactions, which could produce desirable
transgressive segregants in subsequent generations.
The overall results of genetic components of variances for seed yield and
other characters revealed that the estimates of dominance component of genetic Abstract
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variance (D) were significant for days to 50% flowering of primary raceme, days to
maturity of primary raceme, number of nodes up to primary raceme, length of primary
raceme, effective length of primary raceme, number of capsules per plant, 100-seed
weight, oil content and seed yield per plant in both F1 and F2 generations except for
number of nodes up to primary raceme in F2 and oil content and seed yield per plant
in F1 generation. This suggested the involvement of dominance gene action in the
inheritance of these traits. The components of dominance effects (H1 and H2) were
significant for all the characters in both the generations except for H2 in case of
effective length of primary raceme in F2 and number of effective branches per plant in
F1 generation suggesting the prevalence of both these dominance components in the
inheritance of all these characters. Further, the magnitude of H1 and H2 components
was higher as compared to D component for all the characters in both the generations
except H2 for 100-seed weight in F1, which was suggested that dominance
components played a pivotal role in the genetic control of all these traits. The results
obtained for genetic components of variance are also in confirmation of predominant
role of non-additive gene action observed under the combining ability analysis in the
present study.
Average degree of dominance (H1/D)1/2 was in the range of over dominance
for all the characters. The ratio of H2/4H1 indicated the asymmetrical distribution of
positive and negative alleles in the parents for all the characters studied in F1 and F2
generations. However, proportion of recessive genes was higher than that of dominant
genes for all the traits except days to 50% flowering of primary raceme for which
dominant genes was higher than recessive genes. The ratio of total number of
dominant to recessive genes in the parents (KD/KR) indicated unequal frequency of
recessive and dominant with more number of dominant genes in all the traits except
for oil content in both the generations in which proportion of recessive genes was
more.
Narrow sense heritability estimate was high for effective length of primary
raceme and 100-seed weight in F1 generation suggesting that selection based on these
attributes would be confer rapid improvement. Moderate heritability was noticed for
number of nodes up to primary raceme, length of primary raceme, number of effective
branches per plant, number of capsules on primary raceme and oil content in F1
generation, suggesting that breeder can get moderate response while considering
above said traits in selection programme. Remaining characters possessed low
estimate of narrow sense heritability.
It can be concluded that sufficient variation was present in the material for
seed yield and its components. Considerable amount of heterobeltiosis and standard
heterosis was observed for most of the characters studied. The crosses JI 368 x RG
2787, DPC 17 x SKI 343 and DPC 17 x JI 353 displayed high magnitude of standard
heterosis, high sca effect along with high per se performance for seed yield per plant
and some of its components. These crosses could be exploited further for obtaining
desirable types in castor. Both additive and non-additive genetic variances were found
important in the expression of all the traits. The non-additive gene action was more
important for all the characters. This suggested that heterosis breeding or biparental
mating would be more suitable for the improvement of these traits in castor.